Measuring the Earth's Wobble
Spin a top on a flat surface and look closely. Unless you are a master of top-spinning or have poor eyesight, you should be able to see it is wobbling. Many things in the Universe spin like a top and many (likely all) wobble, including the Earth.
From the position of water in the oceans to the currents of air and the gravity of the sun and the Moon, the Earth’s axis of rotation wobbles. It isn’t easy to locate a single point moving at 350 m/s when the center it is moving around is also moving. Traditionally the means to measure the wobble of the Earth involved determining the direction from the Earth to specific quasars in the very distant Universe. This is a very complicated process though and requires the assumption of the quasars not moving. If they are moving, then the measurements are systematically flawed.
In the 90’s though, some researchers proposed a way to directly measure the rotation of the Earth without such assumptions. This new method, built by Technische Universitaet Muenchen, uses lasers moving in a ring-like shape; one beam travels in the direction of the Earth’s rotation and the other moves in the opposite direction. As the mirrors reflecting the light are moving with the Earth while the light is moving independent of it, the Doppler Effect occurs. This is the well-known phenomenon where the pitch of a sound varies based on the speed the observer is moving relative to the sound’s source. The lasers are affected differently because they are traveling in opposite directions. This allows the exact rotational speed of the Earth at the latitude of the setup to be measured.
The researchers envision the apparatus being perfected to the point of operating continuously for years, thereby enabling a scientist to simply walk down some stairs to find out how fast the world is spinning.